A 1944 film by Soyuzmultfilm; made in the Soviet Union in the darkest days of World War 2. See its page at animator.ru for more info (though they got the year of release and some of the crew wrong, unfortunately): http://animator.ru/db/?p=show_film&fid=2941
This film is in the public domain in Russia. And here is my proof: http://www.rosculture.ru/movies_list/listing/show/?id=11581 (that's the film on the Federal Agency of Culture and Cinematography list of Russian films in the public domain)
The English subtitles were created by myself (be sure to download the .srt file!). Here's the direct link: http://ia350627.us.archive.org/3/items/Russian_animation_The_Stolen_Sun./kradenoe_solntse_1943.srt
The translation can only be described as adequate though; after all, the original text is classic children's poetry.
based on text by Korney Chukovsky
Director: Ivan Ivanov-Vano
Assitant director: Aleksandra Snezhko-Blotskaya
Composer: Yu. Nikolskiy
Sound operator: S. Renskiy
Film is PD in Russia; this version is from a DVD containing public domain cartoons by the company Soyuz.
I have watched a lot of old cartoons from the United States but was not aware that there were more cartoonists like Walt Disney or Hanna & Barbara. Maybe someone can provide more information because this cartoon is a beauty and probably there are hundreds like this in the former Sovjet Union.